Device for measurement of thrust and torque in propeller shafts



Sept. 26, 1944. B F, LANGER ET AL 2,359,125

DEVICE FOR MEASUREMENT oF THRUST AND TORQUE IN PROPELLER sHAFTs FiledJuly 12. 1940 2 Sheets-Sheet 2 A'ITORNEY Speedy/Velaz- Sha t PatentedSept. 26,1944

UNITED. STATES PATE1-11-- OFFICE DEVICE F! MEASUREMENT 0F msUST ANDTOMU! 1N mm SHAFT Bernard F. Langer. Pittsburgh, and Harry c.

Werner, Forest Hills Pa.

house Electric t 'Manufacturing Company,- Eaat Pittsburgh, Pa.. acorporation of Pennsyl-v nm.

Our invention relates to a metering device for measuring torque andthrust eithersingly or simultaneously of a drive shaft.

In many applications wherein a drive shaft drives a propeller such as inships and in airplanes, it 'is extremely important to know thesimultaneous values of torque and thrust in order to correctly designthepitch and other such details of the propeller blades so as to design forvmaximum eiilciency. that is, maximum forward for a particular propellertorque at a par-- thrust ticular An object of our invention is toprovide means' including a magnetic strain gauge and electrical bridgecircuit for measuring simultaneously the values of torque and thrust ofa drive shaft at any particular instant.

Another object of our invention is to provide a novel means of mountingmagnetic strain power of a propeller shaft and the ratio of the formerto the latter, namely, the emciency of the propeller.

Other objects and advantages will become more apparent from a study ofthe following specification when considered in conjunction with theaccompanying drawings, in which:

Figure l is a side view partly in cross section of a propeller driveshaft showing the means of mounting the magnetic strain gauges: A

Fig. 2 is a top view of elements of a strain gauge which indicatesthrust showing yieldable means for supporting the relatively movableparts of the strain gauge to arms which spaced portions of the driveshaft:

Fig. 2a is the same as Fig.) except that .the arms are relativelydisplaced as the result of torque on the drive shaft.

Fig.3isaschematicshowing ofacontrol of'iaearxve shaft and n.111 erect.another view oi' the structure shown in Fig. 2; and

Fig. 5 is a schematic showing of a system accordance with our inventionfor reading horsepower and emciency.

In the testing of propellers to determine the correct angle or pitch ofthe blades and otherV features of propeller blade design, it isextremely important to measure torque applied to the propeller shaft andthe axial compression of the shaft produced by propellerssimultaneously. In accordance with our invention, we mount mag- !Iti mlmum on the drive shaft in such a manner that they will indicate relativedisplace-- ment between portions of the drive shaft so as to be ameasure of either torque or thrust or both torque and thrust,-as willappear more clearly hereinafter.

Referring more particularly to Figure 1, numeral 'I denotes a propellerdrive shaft; a portion of which is hollow in construction, that is, theportion shown in the'drawings. Upon which is mounted the strain gaugeassemblies. A pair of magnetic strain gauges 2 and 3 are mounted ondiametrically opposite sides of the drive shaft by means of arms 1-andi-l. respectively,

are secured to which arms are rigidly secured to outstanding annularportions l and l, respectively, which are integral with the drive shaft.Portions l and 9 Y Amay be either machined out of the drive shaftscribed. A complete description of one suit--` able form of strain gaugecan be found in the copending applications of E. H. Lamberger and B. F.Langer, illed April 18, 1939, Serial No. 268,-

500. now Patent No. 2,275,532. issued March 10,

1942, entitled Oil well strain gauges and that of B. L. Burgwin and B.F. Langer, flied February 25', 1939, Sel'il No. 258,510, 110W Patent No.

2,231,702, issued February 11, 1941, entitled` Strain gauges, Briefly,the strain gauge as will be seen from an inspection of Fig. 3 comprisestwo relatively, movable elements, the first being a pair oi E-shapedcores il interconnected by nonmagnetic material (not shown) upon whichcores are mounted a pair of impedance coils Ii and I2 and the secondbeing a magnetic piece Il which is normally equidi'stantly spacedfromthe proiecting ends o f the cores sothat `movement towards one ofsuch ends and away from the other of such ends will change the relativeimpedance of the two coils. By connecting these two coils to animpedance or resistance coil I4, and by connecting a suitable indicatingor recording meter I5, such as an alternating current milliammeter, to acentral point between coils II and I2 and to a central portion of coilI4, it will be readily apparent that an electrical bridge is formed inwhich each half of coil I4 forms a leg and each coil II and I2 formsanother leg and in which meter I5 is included in the neutral leg. Bysuitably Calibrating meter I5 in pound units, for example, the thrust orcompression of the drive shaft as the result of propeller thrust can bereadily measured.

In accordance with the showings of the abovementioned patents, it willbe apparent that the relatively movable parts I and I3 of the straingauges are respectively connected intermediate portions of the apparatusbeing examined. For example, the cores I0 of the gauge may be secured tothe part and the armature I3 to the part 4, or vice versa, wherebyrelative movement between the parts 4 and 5 due to axial thrust will cause relative movement between the parts I Il and I 3 of the gauge.

Referring again to Fig. 1 which shows only a part of the connectionsillustrated in Fig. 3 (the meters Aand external impedance coils beingomitted for simplicity), it will be noted that the strain gauges 2 and 3are connected to slip rings Il and I9 which slip rings are insulatinglysecured by rings I1 and I1' to the drive shaft. A pair of currentcollectors or brushes Il' and IS are connected to a source ofalternating current (not shown). Slip rings29 and 30 are connected to acommon tap to each of the pair of gauges 2--3 and 23-23'. While we haveshown a pair of magnetic strain gauges supported at diametricallyopposite portions of the drive shaft, we wish to Vmake it clear thatonly a single'magnetic strain gauge would be suilicient to indicatethrust. However, in order to compensate for bending of the shaft, weprefer to use two or even more magnetic strain gauges which aresupported at equally spaced locations around the circumference of thedrive shaft so that upon bending of the drive shaft, some would tend torecord a value which is greater thanthe actual thrust and the otherswill tend to record a value which is less than ,the actual thrust,thereby compensating each other and effecting a resultant true readingof the thrust on the drive shaft. It will be noted that the relativelymovable portions I. and lI3 of the strain gauge could be rigidlysecured. to

arms 4-5 and .-1. However, this introducesl an error in the event thatthere is torque on the driveA shaft at the same time that there isthrust, in which case the torque would tend to longitudinally displacearms 4 and i or arms l and 1, hence tending to give a reading on thethrust gauge which is a function of both thrust and torque instead ofthrust alone. Since the strain of the shaft is ordinarily greater intorque than in thrust the torque responsive strain gauges are adjustedto provide a greater amount ofrelative movement between the armature andcore members, than are the thrust responsive strain gauges, hence, thethrust responsive strain gauges are usually more sensitive to slightstrains than the torque responsive strain gauges. In addition shaftshortening due to torque or shaft wind u p is easily detected by thethrust responsive strain gauges since the strain is substantially 'in adirection which the thrust strain gauges are adjusted to detect.straining of the shaft as a result of tension or` compression stressesis not readily detected by the torque responsive strain gauges becausethe strain is at substantially a right angle to the strain resultingfrom torque and, as previously mentioned, the torque strain gauges arenot adjusted as finely as the thrust strain gauges.

In order to overcome this tendency of the strain gauges to respond toshaft strainsother than those they are positioned to detect,particularly in the case of the thrust strain ga les, we have provided ayieldable interconnec ng means such as shown in Figs. 2 and 4 comprisedessentially of a plurality of stiff spring elements 20, 2| and 22. Whilespring elements such as", 2l and 22 are also shown on the torque respon-,sive strain gauges 23 and 23', these are notabusolutely necessary andmay be omitted since the error introduced by virtue of thrust isnegligible. The eect of these spring elements will be to provide an axisof movement A-A, Fig. 4, about which theends of the magnetic straingauge move as a pivot in response to a strain resulting from torquedeveloped in the drive shaft in the case of the thrust strain gauges,and in response to a shaft strain resulting from thrust in the case ofthe torque strain gauges. Fig. 2a shows the manner in which the springelements supporting a thrust strain gauge flex as the result of torque.In this manner the thrust sensitive strain gauge will be responsive tothrust alone and not to torque in addition. An outstanding advantage inusing our yieldable interconnecting means instead of an ordinary hingedjoint is that no friction at the joint, which is variable in nature,will be encountered and which would introduce error in the system. Sofar only the means of l measuring thrust has been considered.

In addition, a similar means for indicating torque is providedcomprising a pair of strain y gauges which are mounted on diametricallyopposite portions of the drive shaft, only one, namely 23, being shown;the other, of course, being hidden on the opposite side of the driveshaft. The ends of strain gauge 28 are secured by arms 24 and 25 tooutstanding ring elements 2l and 21 of the drive shaft, but atperipherally as well as longitudinally spaced points. Furthermore, thestrain gauge is mounted peripheraliy instead of longitudinally of thedrive shaft. The electrical strain gauge is schematically indicated as23 and 23' in Fig. 3, representing bothrpairs of coils onv diametrlcallyopposite portions of the drive shaft, and the torque gauge or meter isdenoted by numeral. 2l which may be of the same type as meter Il, butwhich is calibrated infootpounds orotherunits oftorque. The electricalconnections for the indication of torque are the same as tho for theindication of thrust The shaft is preferably made hollow so that bysuitable choice of the diameter and wall thickness the deflections inall four gauges can be brought to a value to which the gauges are welladapted withoutover-strsing the shaft material. For example, in a solidshaft the compressive stress would probably be small comparedtothetorsionalstresabutbyincreasing the diameter of the shaft andmaking it hollow, the ratio of torsional stress to compressive stressisreduced.'lftheresultlnsshafthssathinwall. it is preferable to leavecollars of thiekermaterial as shown in Fig. l for attachment of thegauges.

Our metering apparatus can also be used for direct reading of horsepoweras illustrated in Fig. 5. The current otherwise flowing through meter 23in Fig. 3, instead, can be rectified by a copper-copper-oxide typerectifier 3i and conducted through the moving coil 32 of a watt meter33,. If thenthe field coil 3l of the watt I through meter Il in Fig. 3can be rectified by g a rectier 3! and conducted through the moving coil3C of a watt meter 31. If then the ileld coil 3l is energized by adirect current generator G2,- the voltage of which is proportional tothe speed .of a speedometer shaft which indicates the linear speed of aship (or an airplane), the watt meter reading will be an indication ofthrust horsepower.

The eiliciency of the propeller is the ratio of thrust horsepower totorque 'horsepower and can be measured in the following way. Watt lmeter31 is provided with a cam 39 of substantially the shape oi' alogarithmic spiral along which a flexible member I is wound. Similarly,the watt meter 33 is provided with a cam member vIl hav-v ing a shapesubstantially the same 'as that of cam 3l and upon which a flexible.member I2 is wound. A scale 43 is graduated in accordance with the scaleof logarithms but is calibrated for indicating eiliciency. That is, thedivisions areV spaced in accordance with a scale of logarithmicvaluesand the values of thrust divided by torque (oremciency) marked adjacentthe positions of corresponding logarithmic values.

If the cam members 39 and 4I are so proportioned that the scale 43 andthe pointer are respectively moved in accordance with the logarithms ofthe displacements of the pointer shafts of watt meters 31 and 33, thepointer 44 will cooperate with the scale 43 to indicate a value which.corresponds to the difference of the logarithms. However, since thediiference of the logarithms of two numbers is equal to the logarithmsof the 'quotient of the numbers the pointer u will indicate incooperation with the scale, the ratio of thrust horsepower to torquehorsepower, namely the efllciency of a propeller. Watt meter 31 movescounterclockwise with increasing horsepower, whereas, watt meter 33moves clockwise'with increased horsepower, as indicated by thescale'calibration.

We are, of course, aware that others, particularly after having had thebenefit of the teach'- ings of our invention, may devise other devicesembodying our invention, and we, therefore, doy `not wish to be limitedto the' specific showings Q made in the drawings and the descriptivedisclosure hereinbefore made, but wish to be limited only by the scopeof the appended claims.

We claim as our invention:A`

1. Apparatus for measuring the ratio of thrust strain" gauge having apair oiimpedance coils wound on supporting cores, which cores aresecured to one of said rings, andasl magnetic piece which is securedlongitudinally and peripherally of the shaft axis on another ot saidring portions, electrical bridge circuits each including a pair ofimpedance arms, each of said magnetic strain gauges having itsimpedancecoils electrically .connected to a, pair ofimpedance arms inone of said electrical bridge circuits, thereby completing saidelectrical bridge circuits, a meter connected in the neutral arm oi'each of said electrical bridge circuits for measuring the amount ofmovement of the magnetic piece with respect to the core structures ofthe associated strain gauge, thereby indicating, respectively, thethrust -ence indeection of said meters and torque on the drive shaft,and a ratio meterl operable in response to the logarithmic differforindicating the ratio of thrustto torque.

2. Apparatus for measuring'the ratio of thrust to torque of a driveshaft, comprising, in combination, a. hollow drive shaft having aplurality `of outstanding ring portions, a pair of magnetic straingauges. each having a pair of impedance coils wound on supporting cores,which cores are secured to one of said rings, and amagnetic piece whichis secured longitudinally of the shaft Y axis on another of saidringportions, a second pair of magnetic straingauges, each having a pairof impedance coils wound on supportingA cores, which cores are securedto one of 'said rings, and a magnetic piece which is securedlongitudinally and peripherally of the shaft axis on another of saidring portions, electrical bridge circuits each including a pair ofimpedance coils,

each of said pairs of magnetic strain gauges,

having the impedance coils thereof electrically connected to a pair ofimpedance arms in one of said electrical bridge circuits, therebycompleting said .electrical bridge circuits, a meter connected in theneutral arm of each ,of said electrical bridge circuits formeasuring theamount of movement of the magnetic pieces with respect tothe corestructures of the pairs of strain gauges, thereby indicating,respectively, the thrust and torque on the drive shaft, and a ratiometer operable in response'to the logarithmic difference in deection ofsaid meters for indicating the ratio of thrust to torque.

3. Apparatus for measuring efficiency of a propeller shaft comprisingmeans including a magnetic strain gauge mounted longitudinally of f theshaft axis and having relatively movable ends connected tolongitudinally spaced portions of said shaft, a second magnetic strainVgauge pe ripherally mounted on said shaft and'having relatively movableends connected to longitudinally and peripherally spaced portions ofsaid shaft, separate circuit means for each of said magnetic straingauges respectivelyincluding an electrical `bridge circuit and adynamometer. type wattmeter having a, movable coil and a stationafrycoil. a direct current generator coupled to said propeller shaft forenergizing the stationary coil of one of said wattmeters'so as to makesuch wattmeterv indicative of torque horsepower, a speedometer shaftwhose rotational lspeed is indicative of the linear speed of the ship, adirect gauge having a pair of--impedance coils wound Y on supportingcores, whichcores are securedto current generator coupled tosaidspeedometer shaft for energizing the stationary coil oi' the other'ofsaid wattmeters so as to make such wattmeter indicative of thrusthorsepower, a

ratio meter responsive to said wattmeters for inating the ratio 4 ofthrust horsepower to torque `propeller shaft comprising a magneticstrain gauge mounted longitudinally of the shaft and having relativelymovable ends connected to longitudinally spaced portions of the shaft, asecond magnetic strain gauge peripherally mounted on said shaft andhaving relatively movable ends connected to longitudinally andperipherally spaced portions of the shaft, means responsive to theamount of movementof the ends of said first gauge and the linear speedof said shaft for measuring the thrust horsepower of said shaft, meansresponsive to the amount of movement of the ends of said second gaugeand the rotational speed of said shaft for measuring the torquehorsepower of said shaft, and means responsive to both of said lastnamed means for indicating` the ratio of thrust horsepower to torquehorsepower.

6. Apparatus for measuring the thrust oi a extending longitudinally ofthe shaft and having relatively movable ends, said gauge comprising acore structure secured to one oi' said ends and a magnetic piece securedto the other of said ends, and means connecting said ends respectivelyto diiferent ones of said ring portions comprising a plurality ofcrossed leaf springs rey spectiveiy having connections with one of saidends and with one of said ring portions to provide a resilient pivotalconnection for each o! said ends with one of said ring portions.

7. Apparatus for measuring the torque of a.

drive shaft comprising. in combination, a hollow drive shaft having aplurality of spaced outstanding ring portions, a magnetic strain gaugeextending peripherally of the shaft and having relatively movable ends.said gauge comprising a. core structure secured to one of said ends anda magnetic piece secured to the other of said drive shaft comprising, incombination, a hollow drive shaft havingk a plurality of spacedoutstanding ring portions, a magnetic strain gauge ends, and meansconnecting said ends .respectively to diii'erent ones of said ringportions at longitudinally and peripherally spaced points including aplurality of crossed leaf springs re spectively having connections withone 'oi said ends and with one of -said ringv portions to provide aresilient pivotal connection for each of said ends with one of said ringportions.

BERNARD F. LANGER. HARRY C. WERNER.

